Consider the example of a rotorcraft flying over terrain that does not have any planned landing zones. A change in flight conditions might require the rotorcraft to and immediately. A flight crew must quickly spot an unplanned landing zone, and lay down an approach gate that allows the rotorcraft to reach the landing zone at a desired glide slope while satisfying minimum clearance requirements.
To make these decisions, the flight crew must process a considerable amount of information very quickly. Assistance with making these quick decisions is highly desirable.